Monarch butterflies are migrating through the St. Louis region right now. Or, at least, they should be.
But so far they have been hard to find, said Tad Yankoski, senior entomologist at the Sophia M. Sachs Butterfly House in Chesterfield.
“We have not seen very many monarch butterflies here at the Butterfly House,” Yankoski said.
Behind the Butterfly House, a garden surrounding a pond holds a lush collection of almost entirely native plants. This is a monarch way station, meant to provide nectar for adult butterflies and milkweed for growing caterpillars to eat.
The garden is supposed to be the perfect place for a monarch butterfly to lay its eggs. Invertebrate keeper Nicole Pruess said it has been alarming to find even this milkweed relatively free of caterpillars.
“It is built for butterflies,” Pruess said. “And we're seeing other butterflies out here, but not really monarchs. So that is concerning to me.”
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For fans of monarchs, this year started on a low note. The scientists who track monarch populations as they overwinter in Mexico announced they had recorded the second-lowest numbers of the butterflies in records going back to the winter of 1993-1994.
Then, there was a reason to be hopeful, said Kristen Baum, director of Monarch Watch and a professor at the University of Kansas.
“The signs were somewhat promising in Texas, so there seemed to be more observations and egg-laying activity reported than what we were initially expecting,” Baum said.
But since then, Baum said she is hearing reports of lower numbers from across the country, which could mean conditions are less favorable for the insect later in the year.
“We'll know more as the migration starts to move through,” she added.
This comes as the U.S. Fish and Wildlife Service is reevaluating adding the monarch to the endangered species list. In 2020, the agency found a listing under the Endangered Species Act is warranted but essentially said there were higher-priority species that needed to be added first.
These monarchs undertake a huge migration each year, passing a baton of survival between generations that start in Mexico, travel through the U.S. to Canada, and then head back to Mexico again.
Along the way, they rely on varieties of milkweed, a native plant, to lay their eggs, fatten up their young and send the next generation on its leg of the journey. Baum said the loss of milkweed has been one of the biggest issues for monarchs.
“If you think about the Upper Midwest, where we have a lot of corn and soybean production, with the Roundup Ready corn and soybeans that removed a lot of milkweed from crop fields,” Baum said. “And then, of course, lots of other urbanization and conversion of natural habitat to other types of land uses.”
On top of habitat loss, climate change is making this journey difficult. It has thrown off the timing of plant flowering, causing some native plants and trees to shift their bloom times by weeks.
“During their migration south, they may travel 2000 miles, and they need to be able to fuel up in the form of sugaring nectar from flowers to get that energy to make it all the way to Mexico,” Yankoski said. “And if the climate has warmed to the point that those flowers they used to rely on for food are blooming a few weeks earlier, well now, when they come through, there's no food for them.”
And climate change is causing some weather extremes like drought or flood during the migration that has caused issues for the monarchs, said Baum.
But there is hope. A single female can lay 100-300 eggs, so monarch numbers could still rebound.
“These animals are very good at adapting and growing in numbers and utilizing resources like milkweed,” Yankoski said. “We hope that we will be pleasantly surprised and see an increase in butterflies that make it back to Mexico this year compared to last year. However, from what we've seen, well, I'm not so confident right now.”
To support the monarchs as they migrate through the St. Louis region, the experts said people can plant native flowers, especially milkweed, in their outdoor space. There are also ways to get involved in citizen science projects tracking monarchs through the program Baum directs, Monarch Watch.
